The disclosure relates to heat pumps. More particularly, the disclosure relates to heat pumps featuring an ejector.
Vapor compression systems have long been used for air conditioning. An exemplary vapor compression air conditioner comprises a refrigerant compressor, an outdoor heat exchanger downstream of the compressor along a refrigerant flowpath, an expansion device downstream of the outdoor heat exchanger, and an indoor heat exchanger downstream of the expansion device prior to the refrigerant flowpath returning to the compressor. Refrigerant is compressed in the compressor. Refrigerant then rejects heat in the outdoor heat exchanger and loses temperature. An exemplary outdoor heat exchanger is a refrigerant-air heat exchanger wherein fan-forced outdoor air acquires heat from refrigerant. By rejecting heat, the refrigerant may condense from vapor to liquid in the heat rejection heat exchanger. Accordingly, such exchangers are often referred to as condensers. In other systems, the refrigerant remains vapor and such are referred to as gas coolers.
The refrigerant expands in the expansion device and decreases in temperature. The reduced temperature of the refrigerant thus absorbs heat in the heat absorption heat exchanger (e.g., evaporator). Again, the evaporator may be a refrigerant-air heat exchanger across which a fan-forced interior/indoor airflow is driven with the interior/indoor airflow rejecting heat to the refrigerant.
Such vapor compression systems may also be used to heat interior spaces. In such cases, the refrigerant flow direction is altered to pass first from the compressor to the indoor heat exchanger and return from the outdoor heat exchanger to the compressor. Such arrangements are referred to as heat pumps.
In addition to simple expansion devices such as orifices and valves, ejectors have been used as expansion devices. Ejectors are particularly efficient where there is a large temperature difference between the indoor and outdoor environments.
An exemplary ejector is formed as the combination of a motive (primary) nozzle nested within an outer member or body. The ejector has a motive flow inlet (primary inlet) which may form the inlet to the motive nozzle. The ejector outlet may be the outlet of the outer member. A motive/primary refrigerant flow enters the inlet and then passes into a convergent section of the motive nozzle. It then passes through a throat section and an expansion (divergent) section and through an outlet of the motive nozzle. The motive nozzle accelerates the flow and decreases the pressure of the flow. The ejector has a secondary inlet forming an inlet of the outer member. The pressure reduction caused to the primary flow by the motive nozzle helps draw a suction flow or secondary flow into the outer member through the suction port. The outer member may include a mixer having a convergent section and an elongate throat or mixing section. The outer member also has a divergent section or diffuser downstream of the elongate throat or mixing section. The motive nozzle outlet may be positioned within the convergent section. As the motive flow exits the motive nozzle outlet, it begins to mix with the suction flow with further mixing occurring through the mixing section which provides a mixing zone.
Ejectors may be used with a conventional refrigerant or a CO2-based refrigerant. In an exemplary operation with CO2, the motive flow may typically be supercritical upon entering the ejector and subcritical upon exiting the motive nozzle. The secondary flow is gaseous (or a mixture of gas with a smaller amount of liquid) upon entering the secondary inlet. The resulting combined flow is a liquid/vapor mixture and decelerates and recovers pressure in the diffuser while remaining a mixture.
U.S. Pat. No. 6,550,265 of Takeuchi et al., issued Apr. 22, 2003, and entitled “Ejector Cycle System” discloses switching arrangements for use of an ejector in a cooling mode and a heating mode. US Patent Application Publication 2012/0180510A1 of Okazaki et al., published Jul. 19, 2012, and entitled “Heat Pump Apparatus” discloses a configuration with ejector and non-ejector heating modes and a non-ejector defrost mode. Additionally, PCT/US2015/030709 of Feng et al., filed May 14, 2015, and entitled “Heat Pump with Ejector” discloses a configuration with alternative ejector and non-ejector heating modes and a non-ejector cooling mode.